1. Field of the Invention
This invention relates to a low temperature sintering ceramic material composition, a process for producing the low temperature sintering ceramic materials, and a ceramic printed plate board using the material as a ceramic substrate. The low temperature sintering ceramic materials of this invention are, for example, particularly useful for a multilayer carrier substrate on which a multilayer substrate IC chip for electronic circuits are mounted.
2. Description of the Prior Art
Requirements have been imposed to improve the packaging density on circuit substrates in accordance with recent advancements in the miniaturization of electronic machines.
In response to such requirements, particularly multilayer wiring using alumina green sheets has already been put to practical use. In this multilayer wiring, alumina green sheets and conductive pattern layers are laminated alternately and then sintered as one body.
Meanwhile, the aforesaid alumina green sheets must be sintered at high temperatures, e.g., in the range of 1500.degree.-1600.degree. C., and therefore the selection of electrode materials have been restricted to metals capable of withstanding high temperatures, such as molybdenum (Mo), tungsten (W) and the like. However, due to the lower electrical conductivity of molybdenum and tungsten rather than silver (Ag) and the like, the miniaturization of the conductive pattern has been limited. Accordingly, alumina could not satisfy the requirements of high packaging density and high speed on an integrated circuit (IC).
Further, conventional low temperature sintering materials capable of being sintered at about 1000.degree. C. have a low thermal conductivity below 0.01 cal/s.cm..degree. C. For example, alumina glass is sintered at about 900.degree. C. and has a low thermal conductivity of 0.006. Further, ICs and transistors which consume large amounts of electric power could not be mounted on a conventional substrate since the temperature of the element would be elevated by heat from the substrate.
If, however, ceramic materials could be sintered at low temperatures, below 1300.degree. C. and exhibit excellent thermal conductivity, the above mentioned problems could be eliminated.
Among conductive pastes which exhibit excellent thermal conductivity, the silver (Ag)-palladium (Pd) type paste cannot be sintered over 1300.degree. C. If the sintering temperature is decreased below 1000.degree. C., such conductive pastes as silver (Ag), silver (Ag)-platinum (Pt), copper (Cu) and nickel (Ni) can be used.
Japanese Patent Laid-Open No. Showa60-18994 discloses a method for producing an enamel substrate for a printed plate board. In this method, an insulating layer is formed by melting a glass power at temperatures over 700.degree. C. The glass powder has no crystal structure since the glass powder is produced by freezing and solidifying a liquid phase (glass phase) quenched from the completely melted state at 1500.degree. C. However, in general, glass and enamel have a thermal conductivity which is inferior to crystal since no crystal structure is contained therein. Thus, when glass materials are used for the printed plate board, the consumption of electricity of the IC must be decreased.